Saturday night is the best time for a fiery object to cross the night sky—of that there is no doubt. This past Saturday was no exception. Countless users took to social media to share videos that showed a fireball hurling over the Iberian Peninsula. At first, users believed that the object was a meteorite, but that turned out not to be the case.
A piece of comet. The European Space Agency’s (ESA) fireball camera detected the object in Cáceres, Spain, on Saturday at 22:46 UTC (0:46 in Spain). ESA’s Planetary Defense Office analyzed the object and believes it was in fact a small piece of a comet that disintegrated in Earth’s atmosphere at a low altitude of 37 miles.
According to ESA estimates, the fireball flew over Spain and Portugal at 28 miles per second (100,662 mph) before burning up over the Atlantic Ocean.
High magnesium content. The Spanish National Research Council (CSIC) analysis concluded that the object hit the upper atmosphere layers with a very flat trajectory, at an angle of 10 degrees above the horizontal line, which increased its brightness and visibility.
The blue hue of some objects that cross the sky–as is the case of the one seen last weekend–may be produced by magnesium-rich minerals, such as olivine and pyroxene, which are common in these kinds of extraterrestrial objects.
Why it’s not a meteorite. A meteorite is a fragment of a meteor that survives its passage through the atmosphere and reaches the surface of the Earth. In this case, despite burning at a low altitude, ESA thinks it’s unlikely that any fragments will be found, due both to the speed of disintegration and its trajectory over the Atlantic Ocean.
From meteor to superbolide. The term “meteor” is used to describe any object that enters the atmosphere and produces a light effect when it burns up from air friction. A bolide (also known as fireball) is a particularly bright meteor, usually brighter than any star in the night sky. There are thousands every year. A superbolide is an extremely bright fireball; they are very rare and light up the sky like daylight.
The object seen on Saturday was classified as a superbolide because it had a magnitude of -16±1, much brighter than a full Moon, according to Spain's Bolide and Meteorite Research Network.
Undetected. Despite the growing number of cameras, radars, and telescopes pointed up towards space, the object wasn’t spotted before it hit the atmosphere. ESA’s Planetary Defense Office will keep investigating the event to determine if there were any reasons for concern.
Image | ESA